The present invention generally relates to medical devices, and in particular, to improved compliant expansion balloons for use with medical catheters.
Compliant inflatable balloons, of the type used with medical catheters, increase in diameter with increasing inflation pressure until the balloon burst pressure is reached, as is well-known to those of skill in the art. Such balloons are especially advantageous when used as an occlusion balloon, or as the securing element of an anchorable guidewire. In both applications, the balloon must be expanded to contact the blood vessel wall. In some treatment procedures, however, the clinician does not know the precise diameter of the blood vessel segment that the balloon must contact. In these situations, the compliant expansion profile of the balloon permits the clinician to make the required contact, by application of increasing inflation pressures to cause increased balloon radial expansion until contact is achieved.
Conventional compliant expansion balloons are generally made of elastomeric materials, such as latex and silicone. Balloons made of these materials utilizing conventional balloon formation techniques suffer from several disadvantages which adversely affect the balloon's performance.
One disadvantage of conventional compliant balloons relates to their elastic response. It is desirable for catheter balloons to have a predictable inflation profile. That is, the balloon should inflate to a certain known size upon application of a specific pressure. Moreover, the balloon should exhibit good elasticity, inflating to approximately the same size upon application of the same specific pressure or volume, even after the balloon has been inflated and deflated multiple times. However, conventional compliant balloons often do not exhibit this desired elastic response, and tend to inflate to larger sizes upon application of the same specific pressure each subsequent time they are inflated. This is because each inflation stretches the balloon, and upon deflation, the balloon does not return to its original deflated size, but instead is somewhat larger. Consequently, upon each subsequent inflation, the stretched balloon inflates to a larger size than before, making it difficult for the clinician to predict the amount of pressure that must be applied to inflate the balloon to the size needed to contact the vessel.
Another disadvantage of conventional compliant balloons relates to their longitudinal expansion. As described previously, compliant balloons tend to increase in radial diameter with increasing inflation pressure. In addition, many compliant expansion balloons also tend to increase in length with increasing inflation pressure. This is an undesirable expansion characteristic, as it creates an unwanted shearing force within the blood vessel, which could lead to vessel trauma.
Accordingly, there exists a need for compliant expansion balloons for use as occlusion balloons on catheters, or as securing members on anchorable guidewires, which have a predictable elastic response, a predictable longitudinal expansion, and a predictable diameter, at different volumes or pressures. In addition, there is a need for methods of making such balloons.